Most mobile device users are aware that sophisticated hardware and software are used to drive their device display. However, far fewer users may realize that providing audio on such a device also raises daunting challenges. For users that employ earphones or headphones when listening to their device, the transduction of audio data into sound is left to the earphone or headphone manufacturer. However, for audio that needs to be projected directly from the device itself, e.g., during a hands-free call, the phone itself must be equipped for the transduction of audio data into sound.
Traditionally, mobile devices have employed simple speaker technology. However, the continuing decrease in device size and weight have lead to an alternative speaker technique, namely, the use of the device display glass itself as a speaker membrane or surface. While this may be referred to as a moving-screen technology, it might more accurately be considered a vibrating-screen technology; these terms may be used interchangeably herein.
In the moving-screen technique, the glass display acts as a transducer for an audio signal. This provides certain benefits, e.g., the user can place his ear essentially anywhere, during a hands-free or ordinary call, and still hear the conversation. However, there are also substantial drawbacks: Glass displays are designed primarily for visual display and not for audio transduction and thus do not inherently posses the properties required for high quality sound reproduction.
Thus, for example, a single transducer applied to a display screen tends to have an audio response characterized by acoustic peaks and valleys. In addition, this type of moving-screen technology often results in poor reproduction of low-frequency audio. Moreover, since the display-screen production process is not adapted to test or control audio-response characteristics, there is substantial variation in frequency response from screen to screen. While these shortcomings can manifest themselves in the form of poor audio quality from the user's standpoint, they may also be severe enough to prevent industry certification or approval of the device.
It will be appreciated that this Background section represents the observations of the inventors, and these observations are provided simply as a research guide to the reader. As such, nothing in this Background section is intended to represent, or to fully describe, any particular prior art.